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1. Field of the Invention
The present invention generally relates to wastewater treatment, and more particularly to an apparatus for enhancing biological and biochemical performance of on-site residential and/or commercial single or multiple compartment septic tank wastewater treatment systems thereby resulting in superior effluent discharge quality.
2. Description of the Background Art.
It has been found that treatment of wastewater for the reduction of biological oxygen demand (BOD), total organic carbon (TOC), and total suspended solids (TSS) can be accomplished using beds of particulate media that act as a carrier for viable bacteria forming the biological reaction. The particulate bed may be a fixed bed, such as the sand bed of a trickling filter, or a fluidized bed wherein the particulate bed functions in a fluidized condition. Fluidized bed biological reactors are very effective wastewater treatment devices due to the extremely high concentrations of viable bacteria maintained within the system. U.S. Pat. No. 4,009,098 issued to Jeris discloses the use of a fluidized bed for BOD removal. U.S. Pat. No. 4,009,099, issued to Jeris discloses the use of a fluidized bed to remove ammonia nitrogen (nitrification), and/or to denitrify in connection with the treatment of wastewater. U.S. Pat. No. 4,322,296, issued to Fan et al., discloses a method for wastewater treatment in fluidized bed biological reactors.
While the use of fluidized bed reactors has resulted in some success in wastewater treatment, constant air control maintenance and adjustment has always been required to maintain the overall combustion (slow oxidation) stoichiometry necessary to ensure that adequate performance is maintained, particularly when experiencing varying loading conditions. While performance may be maintained, monitored, and controlled in large-scale wastewater treatment facilities through the use of sophisticated controls as seen in typical sequential batch reaction systems, the availability and use of sophisticated controls in smaller scale applications, such as residential and/or on-site commercial treatment facilities, has not proven practical or cost effective. Accordingly, residential and smaller scale wastewater treatment facilities often function at less than optimal performance and thus fail to adequately treat wastewater prior to discharge into the surrounding environment.
Additionally, since any typical aerobic wastewater system is performing useful work (consuming dissolved oxygen) only when operating in an aerobic mode, use of automatic controls for the purpose of creating sequential batch reaction (typically necessary to force an air deprived or anoxic denitrification cycle) takes away significant useful time, and therefor overall treatment capacity, from a given daily period.
By way of the following example a proper stoichiometric balance is demonstrated. For instance, if a household were to generate 1000 liters/day of wastewater (264 gallons), and said wastewater contained approximately 200 mg/liter BOD (Biological Oxygen Demand), then the daily oxygen demand is 1000 liters/dayxc3x97200 mg/liter=200,000 mg/day BOD. It should be noted that the calculation is measured in BOD, as opposed to CBOD, due to the fact that, in a typical septic tank almost 100% of the Total Nitrogen is in the form of ammonia which would not be included in a measurement of CBOD.
According to the system disclosed herein, air is introduced into the wastewater to elevate the dissolved oxygen content from close to zero to 3.5 mg/liter or higher. In addition, the flow rate through a fluidized bed oxidation chamber is specifically adjusted such that substantially all of the dissolved oxygen is consumed. By way of example, at a flow rate of 40 liters/minute, dissolved oxygen will be consumed at a rate of approximately 200,000 mg/day as follows: At a flow rate of 40 liters/minutexc3x973.5 mg/liter dissolved oxygenxc3x9760 minutes/hourxc3x9724 hours/day=dissolved oxygen consumption is 201,600 mg/day. Thus, in suitable biological presence an application of just the right amount of oxygen (oxidizer), presented with just the right amount of fuel (BOD), near perfect oxidation, and therefor system performance, can be observed. Measurement of dissolved oxygen factor of water entering the fluidized bed minus dissolved oxygen factor of water exiting the fluidized bed times the flow rate will provide a realistic calculation of performance.
There remains a need for an improved wastewater treatment system capable of performing multiple functions to optimize system performance while requiring no day-to-day adjustments based upon daily loading, as well as no particular scheduled maintenance. There further exists a particular need for a device that can metabolize Carbonaceous Biochemical Oxygen Demand (CBOD) and protein compounds of Organic (Kjeldahl) Nitrogen, while simultaneously reducing Total Nitrogen levels by first converting Ammonia to Nitrite through the use of aerobic facultative Nitrosomonas bacteria, and subsequently converting Nitrite to Nitrate using aerobic facultative Nitrobacter. Simultaneous denitrification must also occur for any such system to completely convert Nitrate to harmless Nitrogen gas. There particularly exists a need for an effective, low-cost, wastewater treatment system for use in conjunction with residential and/or light commercial wastewater devices (e.g. septic tanks) that provides highly effective performance while requiring minimal controls or scheduled maintenance.
The present invention provides a wastewater treatment system for use with a conventional septic tank, or other small-scale wastewater treatment system, for enhancing wastewater treatment without requiring complex control or maintenance limitations. The system of the present invention incorporates a plurality of primary functions that combine to oxidize, nitrify, denitrify and remove water borne total dissolved solids prior to effluent discharge. Included is a fluidized-bed reactor containing biofilm attached to carrier particulates for use in the purification of wastewater. The fluidized-bed reactor is configured to include two distinct regions, namely a xe2x80x9clowerxe2x80x9d aerobic region and an xe2x80x9cupperxe2x80x9d anoxic region, during normal operating conditions. The lower aerobic region uses aerobic facultative bacteria to oxidize Carbonaceous Biochemical Oxygen Demand (CBOD), organic (Kjeldahl) nitrogen, and ammonia while consuming the dissolved oxygen in the water. Simultaneously, denitrification occurs in the upper anoxic region of the same bed at the same time. The creation of an additional anoxic region is provided elsewhere in the system for times when the workload is decreased and therefore dissolved oxygen consumption of the reactor becomes too low to maintain an anoxic state in the upper region of said reactor. This additional anoxic region assures effective denitrification under all operating conditions.
In addition, the system disclosed herein can be easily installed either inside (in-situ) a septic tank structure, or nearby, in an above ground configuration (ex-situ) in conjunction with an existing septic tank, thereby allowing for an extremely universal application.